Recently, digital cameras using an image sensor technology such as CCD (Charge Coupled Device) or CMOS (Complementary Metal-Oxide Semiconductor) have become very popular. The digital camera is commercialized as a camera-only-product and typically is mounted in a hand-held terminal such as a mobile phone or PDA (personal digital assistant).
However, the central processing unit of the hand-held terminal does not have the high clock speed and memory capacity of a personal computer, which may limit the hand-held terminal's ability to perform digital image processing. Moreover, development trends toward reduced thickness and size of the hand-held terminal results in a spatial limitation with respect to the size of additional hardware and devices, such as a camera, that can be mounted in a hand-held terminal. Accordingly, there are limitations in the number and types of image processing techniques, such as, for example, a digital image stabilization technique for preventing deterioration of a digital image caused by shaky hands of a photographer, that can be incorporated in a camera-only-product of a hand-held terminal.
A typical digital camera supports an auto exposure mode, where EV (Exposure Value) is automatically changed depending on the luminance of the location where a photograph is taken. EV is increased in dark places and decreased in bright places.
However, an increase in EV causes an increase in exposure time. This can result in an image blurring phenomenon since a small tweak in a focus caused by shaky hands is reflected in a photograph. Known image stabilization techniques were introduced to prevent the image blurring phenomenon, such as, for example, DIS (Digital Image Stabilization), EIS (Electrical Image Stabilization) and OIS (Optical Image Stabilization).
The DIS technique detects/compensates for the shaky-hands effect using an image signal stored in a memory. The DIS technique detects a motion vector using an image signal that is generated in an image pickup device and stored in a memory, and changes a read timing of the memory using the detected motion vector to compensate for shaky hands. The DIS technique has an advantage of simple image stabilization. However, because a read timing of a memory is changed, the size of an image readable from the memory is equal to that of an effective pixel area. Thus, the DIS technique expands an image read from the memory by digital zoom and plays/records the expanded image, which results in deterioration of image quality.
The EIS technique detects/compensates for the shaky-hands effect using an angular velocity sensor and a high pixel image pickup device. The EIS technique detects the amount and direction of hand tremor using a horizontal/vertical angular velocity sensor, and changes an output timing of a high pixel image pickup device using the detected amount and direction of hand tremor to compensate for shaky hands. As an output timing of a high pixel image pickup device is changed, the size of an image that is composed of an image signal output from the high pixel image pickup device is equal to that of an original image. This occurs because the high pixel image pickup device used in the EIS technique has more pixels than the number of effective pixels. Thus, the EIS technique can reduce the deterioration of image quality. However, the EIS technique requires an angular velocity sensor and a high pixel image pickup device, which results in an increase in manufacturing costs.
The OIS technique detects/compensates for the shaky-hands effect using an angular velocity sensor and a prism. The OIS technique uses the same technique as the EIS technique in that the amount and direction of hand tremor is detected using a horizontal/vertical angular velocity sensor. However, the difference is that the OIS technique uses a prism capable of changing a path of light incident upon an image pickup device to compensate for shaky hands. The OIS technique does not result in a deterioration of image quality and does not require a high image pickup device. However, the OIS technique requires an angular velocity sensor and a prism, which increases both the size and manufacturing costs of a photographing device. Further, the OIS technique has difficulty controlling the prism.